SEX AND AGE DIFFERENCES IN IMMUNITY TO INFLUENZA (SADII) IMMUNE RESPONSES RESOURCE CORE SUMMARY Under the leadership of Dr. Patricia Gearhart (Director) and Dr. Sabra Klein (Co-Director), the Immune Responses Core will provide the serological, cellular, and genetic assays that will be necessary for the accurate, and consistent measurement of sex and aged differences in immune responses to influenza vaccines and viral antigens. The Core will provide serological assessment of antibody responses to influenza vaccine and virus antigens for Research Projects 1, 2, and 3. The serological assessments will include microneutralization assays, hemagglutinin (HA) inhibition assays, and ELISAs to detect IgG that is specific for diverse influenza virus proteins, including HA, neuraminidase (NA), and the M2 protein as well as IgM and IgG isotypes to evaluate somatic hypermutation and class switching. The Core will also be responsible for conducting cellular analyses of antigen-specific (i.e., HA, NA, M2) B cells in humans and mice by flow cytometry using the MMI BD Immune Function Core facility. Particular attention will be paid to the quantification of plasmablasts and germinal center cells, including memory B cells and the recently characterized Age-associated B cells (ABCs). Finally, using the MMI Genomics and Analysis Sequencing Core, we will analyze the transcriptional variation associated with sex and age by transcriptional profiling antigen-specific B cells (i.e., plasmablasts) in humans and mice (Projects 1, 2, and 3). The transcriptional analyses will include using deep sequencing to quantify transcriptional activity in plasmablasts to evaluate the pathways differentially regulated by age and sex. Following repeated exposures to influenza antigens through infection and vaccination, an immune repertoire develops that reflects clonal selection during the primary response and recall and somatic rearrangement of VH genes following subsequent exposures, including following vaccination. V gene repertoires will be compared and analyzed for sex and age associated differences following vaccination. Together, the SADII Immune Responses Core will provide an in-depth analysis of how sex, age, and frailty alter antibody responses, B cell phenotypes, and B cell genotypes in response to influenza vaccination. With serological, cellular, and genomic assay capabilities, the SADII Immune Responses Resource Core can provide services to investigators interested in characterizing influenza virus-specific immune responses, which is currently not available at Johns Hopkins, and to SCOREs at other institutions that are seeking to measure inflammatory and immune markers of diverse diseases, beyond influenza.